UPPER TRIASSIO SPECIES. 99 



From this structure, each side of the fossil looks very much as if there were 

 two large, sharply-angular lateral lobes, where there is really only one.* 



The only specimen of this species I have seen belongs to the Museum 

 of the General Land-Office at Washington. It is an internal cast, com- 

 posed of a deep brownish-red oxyd of iron, but shows all the characters of 

 the species, excepting the surface-markings (if there were any), very clearly. 



Locality and position. — It is only known that the specimen came from 

 New Mexico. From its affinities, it would seem to be of Carboniferous age. 



UPPER TEIASSIO SPECIES. 



MOLLUSOA. 



BRACHIOPODA. 



DISClNIDiE. 



Genus DISCINA, Lamarck. 



DisciNA, sp. undetermined. 



Plate 10, figs. 3, 3 a. 



I only know this shell from two specimens of the under valve, and 

 these show only the inner side. They have a subcircular or broad subovate 

 outline, being slightly narrower posteriorly than in front. The anterior 



* The contrast in the structure of the septa of the typical Goniatites, such as 

 G. sphccricus, De Qaan, and the species here described, with their deep, acutely 

 angular lateral lobes, and those older species, such as G. expansus or Marsellensis, 

 Vanuxem, with the septa making merely a broad backward curve across each side, 

 without any lateral lobes, is very striiiing. It may therefore be convenient to separate 

 these more simple types (the Nautilini of authors) as a distinct subgenus on this 

 structure of the septa and other characters. I would therefore propose for this group 

 the subgeneric name Agoniatites, with Goniatites [Agoniatites] expansus^ or Marsellensis, 

 of Vanuxem, as the type. It is probable, however, that there are, among the known 

 species with this simple structure of the septa, forms that might be properly separated 

 from the group including G. expansus on other characters, as that species presents 

 some striking peculiarities in its development, the young having its periphery rounded 

 with a double groove and a ridge between, and the sides marked with arching undula- 

 tions, while in the adult, the undulations become obsolete, and the periphery flattened, 

 with distinct angles. G. Bohcmicus of Barrande belongs to this group. 



